During some conditions, turbocharged direct-injection engines may generate increased soot. For example, during some conditions, fuel may not sufficiently mix with air before combustion, for example due to reduced turbulence. Such phenomena may occur when the engine is operating at high speed and/or high loads.
The inventors herein have recognized that one approach to address such an issue may be to utilize a particulate filter in the exhaust. However, regeneration of the filter in the exhaust of a spark-ignited engine aimed at stoichiometric emission control raises numerous issues. As just an example, sufficient excess oxygen for regeneration in the exhaust may result in increased NOx emissions.
Accordingly, systems and methods for controlling regeneration of a particulate filter positioned downstream of an engine in a vehicle are provided herein. One exemplary method includes, during combusting engine conditions, directing exhaust from the engine to a three-way catalyst and then to a particulate filter positioned downstream of the three-way catalyst. The method also includes, during non-combusting engine conditions and while the vehicle is in motion, directing fresh ram-air to the particulate filter to regenerate the particulate filter.
By using ram-air to regenerate the particulate filter, the particulate filter can be regenerated during vehicle motion. Furthermore, a ram-air entrance to the exhaust passage may be downstream of one or more other emission control devices, thus reducing an effect of excess oxygen on the one or more other emission control devices.
The present description addresses various aspects of such regeneration and associated control, including adjusting operation during and/or after an engine shutdown to enable regeneration under such conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.